Process of making alluminum coated ferrous bodies



PROCESS OF MAKING ALUMINUM CGATED FERROUS BODIES Marshall G. Whitfield,Garden City, and Victor Sheshunoif, .iericho, N. Y., assignors toWhitfield & Shesltunott, Incorporated, Garden City, N. Y., a corporationof New York No Drawing. Application August 4, 1951, Serial No. 240,447

3 Claims. (Cl. 117-114) This invention relates to an improved method ofcoating ferrous metal articles, and more particularly to a method forcontrolling the formation of a bond between ferrous metal bodies andaluminum and its alloys.

When molten aluminum-containing metal is applied either as a coating ora layer to a ferrous metal surface under proper conditions, thealuminum-containing metal combines substantially at once with theferrous metal surface. It is also recognized that a ferro-aluminum alloyis formed at the interface between the ferrous body and the layer orcoating of the aluminum-containing metal, such alloy bonding the coatingto the body.

While the formation of a ferro-aluminum alloy at the interface isnecessary to obtain a permanent bond between the ferrous metal surfaceof the body and the coating or layer of aluminum-containing metal, wehave now dis-- covered that the presence of this alloy in large amountsimpairs the strength of the resulting composite structure, and thecontrol of the thickness of this bonding alloy is critical to thestrength and permanence of the bond. In general, the bonding alloyformed at the interface is brittle in nature and the strength of theresulting bond, insofar as subsequent hot and cold working operations isconcerned, is dependent to a large extent on the thickness of suchalloy. We have found that for most conditions of rigorous working of theresulting laminate of ferrous metal and aluminum or aluminum alloy, thatthe thickness of the bonding alloy formed at the interface should notexceed about 0.6 mil and preferably should not be in excess of 0.5 mil.By limiting the thickness of the bonding alloy to not more than 0.5 milwe have observed that the resulting laminate can successfully withstandheat-treating and rolling operations which cannot be efiicaciouslycarried out with laminates having a thicker bonding alloy at theinterface. In accordance with the process of this invention, the depthof the bonding alloy may be controlled by incorporating into the ferrousmetal body to be coated a small proportion of at least one of the metalsof the sixth periodic group. In this group, molybdenum and tungsten havebeen found particularly effective. The selection of the particular metalor metals of this group to be employed is largely determined by the useto which the coated body is to be put. However, since the percentage ofthese heavy metals used for alloy control is relatively small, the ironsand steels used in many arts can readily accommodate one of these metalsin the small quantity required without impairing the utility of thearticle, and in fact many irons and steels utilizing such metals fortheir physical attributes can be coated with aluminum oraluminum-containing alloys according to this invention without requiringspecial addition of the alloy-controlling metal for that purpose. Forinstance, commercially available steels containing either molybdenum,tungsten, or both, for example up to 5% or more of molybdenum, or 20% ormore of tungsten, may be successfully employed in the practice of thisinvention without the necessity of adding further amounts of such metalsas in the case of low carbon or loy alloy steels.

atent In the case of low alloy steels containing about 1% of eithermolybdenum, or tungsten, the alloy bond thickness resulting from dippingsuch steel in molten aluminum of commercial purity has resulted in abond alloy having a thickness not appreciably greater than about 0.4 to0.6 mil, whereas a plain carbon steel dipped under the same conditionsshowed an undesirable alloy bond thickness of substantially 2.0 to 2.5mils. Very small additions, i. e. from a trace to an amount notmaterially exceeding 1% of tungsten 0r molybdenum to a medium or lowcarbon steel resulted in a substantial reduction in the thickness of thealloy bond layer and for bodies which are to be subjected to subsequentrigorous treatment we have found that the thickness of the alloy bondshould preferably be less than 0.4 mil, indicating that for manypurposes the percentage of molybdenum or tungsten need not materiallyexceed 1% by weight of the steel.

While molybdenum and tungsten vary in efiiciency in controlling thethickness of the bonding alloy the combination of these metals as alloybond controllers may advantageously be employed. We have observed thatalthough in certain molten aluminum-containing metals the bolybdenumtends to go into solution, nevertheless, molybdenum helps to control thethickness of the bonding alloy when coating molybdenum-containing steelsdesigned for special purposes.

The term aluminum as used herein includes aluminum as well asaluminum-containing alloys, and particularly aluminum-base alloys, sincethe presence of the aforementioned metals in the steel article to becoated controls the alloying action between the ferrous metal of thebody and the coating or layer of aluminum or aluminum alloy regardlessof the presence of metals or non-metals that may be in the aluminum oraluminum alloy.

In carrying out the process of this invention, the ferrous metal body isalloyed with the indicated small percentage of molybdenum or tungsten,or combination thereof, whenever it is desired to control the thicknessof the bonding alloy formed at the interface between the surface to becoated and the aluminum. The amount of the aforementioned bond-controlmetal determines the depth of the bonding alloy, without requiring theextremely accurate time and temperature control heretofore required forthat purpose. For example, the temperature of the aluminum-containingmetal can be maintained between the melting point of such metal andabout 1350" Fahrenheit. With such alloy thickness control the strengthof the bond is greatly augmented, since the bonding alloy is reduced inthickness and thus enables the composite metal article to be workedeither hot or cold, or be subjected to wide temperature fluctuations, orboth, without impairment of the bond.

Although a preferred method of controlling the depth of the alloyformation between the ferrous metal surface and aluminum-containingmetals has been described herein, it is to be understood that the methodof this invention may be used to control the depth of the alloying bondby pro-portioning the percentage of the alloy inhibiting metal in thesteel so as to obtain an alloy at the interface of any desired thicknessbetween that obtained without the use of the aforementioned heavy metalsand that obtained with the maximum percentage which secures a bond ofminimum safe thickness for rigorous treatment of the composite article.It is also to be understood that other variations in the invention maybe made within the scope of the appended claims.

This application is a continuation-in-part of our application Serial No.757,920, filed June 28, 1948, and now abandoned.

We claim:

1. In the process of bonding a coating of aluminum to a plain carbonsteel base by dipping said plain carbon steel base into a bath of moltenaluminum to form a coating of aluminum thereon and a ferro-aluminumbonding alloy at the interface between said plain carbon steel base andsaid aluminum coating, the improvement comprising initially alloying insaid plain carbon steel base about 1 per cent of a metal selected fromthe group consisting of molybdenum and tungsten, immersing the resultingalloyed body into a bath of molten aluminum maintained at a temperaturenot above about 1350 F. for a period to form the desired thickness ofsaid coating, said bonding alloy being simultaneously formed andautomatically controlled to a thickness not in excess of 0.6 mil,irrespective of the time of immersion in said molten bath.

2. In the process of bonding a coating of aluminum to a low alloy steelbase containing about 1 per cent of a metal selected from the groupconsisting of molybdenum or tungsten by dipping said low alloy steelbase into a bath of molten aluminum to form a coating of aluminumthereon and a ferro-aluminum bonding alloy at the interface between saidcoating and said base, the improvement comprising immersing said lowalloy steel base into a bath of molten aluminum maintained at atemperature not above about 1350 F.- for a period to form the desiredthickness of said coating, said bonding alloy being simultaneouslyformed and automatically controlled to a thickness not greater thanabout 0.4 to 0.6 mil, irrespective of the time of immersion in saidbath.

3. In the process of bonding a coating of aluminum to a ferrous metalarticle by dipping said article into a bath of molten aluminum to form acoating of aluminum thereon and a ferro-aluminum bonding alloy at theinterface between said ferrous metal article and said coating, theimprovement comprising initially alloying in said ferrous metal articleabout 1 per cent of a metal selected from the group consisting ofmolybdenum and tungsten, immersing the resulting alloyed body into abath of molten aluminum maintained at a temperature above the fusiontemperature of said aluminum but below 1350 F., for a period to form thedesired thickness of said coating, said bonding alloy being therebysimultaneously formed and automatically controlled to a thickness not inexcess of 0.6 mil.

References Cited in the file of this patent UNITED STATES PATENTS1,695,594 Lagenbert et al Dec. 18, 1928 1,706,130 Ruder Mar. 19, 19291,881,064 Sayles et al. Oct. 4, 1932 1,929,252 Morris Oct. 3, 19332,300,400 Axline Nov. 3, 1942 2,455,457 Whitfield et al Dec. 7, 19482,512,141 Ma et a1 June 20, 1950 2,588,421 Shepard Mar. 11, 19522,682,702 Fink July 6, 1954 2,697,869 Kingston Dec. 28, 1954 FOREIGNPATENTS 428,855 Great Britain May 21, 1935 OTHER REFERENCES Alloys ofIron and Tungsten, page 137. Edited by Gregg, published in 1934 by theMcGraw-Hill Book 00., New York, N. Y.

1. IN THE PROCESS OF BONDING A COATING OF ALUMINUM TO A PLAIN CARBONSTEEL BASE BY DIPPING SAID PLAIN CARBON STEEL BASE INTO A BATH OF MOLTENALUMINUM TO FORM A COATING OF ALUMINUM THEREON AND A FERRO-ALUMINUMBONDING ALLOY AT THE INTERFACE BETWEEN SAID PLAIN CARBON STEEL BASE ANDSAID ALUMINUM COATING, THE IMPOVEMENT COMPRISING INITIALLY ALLOYING INSAID PLAIN CARBON STEEL BASE ABOUT 1 PER CENT OF A METAL SELECTED FROMTHE GROUP CONSISTING OF MOLYBDENUM AND TUNGSTEN, IMMERSING THE RESULTINGALLOYED BODY INTO A BATH OF MOLTEN ALUMINUM MAINTAINED AT A TEMPERATURENOT ABOVE ABOUT 1350* F. FOR A PERIOD TO FORM THE DESIRED THICKNESS OFSAID COATING SAID BONDING ALLOY BEING SIMULTANEOUSLY FORMED ANDAUTOMATICALLY CONTROLLED TO A THICKNESS NOT IN EXCESS OF 0.6 MIL,IRRESPECTIVE OF THE TIME OF IMMERSION IN SAID MOLTEN BATH.